Apparatus for coating



1956 E. P. MILLER APPARATUS FOR COATING 2 Sheets-Sheet 1 Flled Nov. 5,1945 a n... DOAR m MM M mo R m NYJ/Q m m u E A A In E ..u u 103 E 9 ow mmdE Nov. 13, 1956 E. P. MILLER 4 2,770,210

APPARATUS FOR COATING Flled Nov. 5, 1945 2 Sheets-Sheet 2 N VEN TOR.

EMERY P. M/ZLE United States Patent F APPARATUS FOR COATING Emery P.Miller, Williams Creek, Ind., assignor, by direct and mesne assignments,to Ransburg Electro-Coating Corp., Indianapolis, Ind., a corporation ofIndiana Application November 5, 1945, Serial No. 626,631

7 Claims. (Cl. 118-7) This invention relates to the deposition of finelydivided material upon an object in an electrostatic field.

In the manufacture of tinned sheet steel, commonly known as tin plate,used extensively for making soldered seam cans, it is the practice toapply a thin coat of oil to the tinned surface of the tin plate, thiscoating generally being applied to the tinned plate or strip before itis cut into blanks for the forming presses. The coating of oil isdesirable as an aid in separating the sheets from the stack and as anaid in securing proper printing in the subsequent lithographingoperation. An excessive coat of oil on the tin plate interferes with theproper stacking of the blanks by causing the sheets to offset,interferes with the subsequent operations of soldering or lithographing,and has other disadvantages.

It is an object of the present invention to apply to the surface of anarticle, a thin coating of liquid.

Another object is to apply to an article a thin continuous coating ofliquid.

Another object is to apply to a continuous web of material a coatingwhich is maintained substantially uniform over large areas.

Another object is the treatment of an article having spaced droplets orparticles of liquid having dielectric properties on the order ofvegetable, mineral or animal oils or molten waxes thereon to causespreading or coalescence of the droplets or particles.

Another object is the provision of an improved process of introducingliquid coating material into an electrostatic field for depositionthereby.

Another object is the proportioning of the speed of a web with relationto the quantity of coating material deposited thereon.

In accordance with one feature of the present invention, a coating isdeposited upon a surface in the form of discrete spaced particles ofliquid, and the coated surface is subjected to an electrostatic field ofsufiicient intensity to spread or coalesce the particles. Preferably thecoating is obtained by precipitating liquid particles upon the surfacein an electrostatic ionizing field or zone, and the coated surface isexposed to an electrostatic field for a sufficient length of time tosecure the desired degree of spreading of the particles. By depositingthe particles upon a moving sheet or article adjacent one end of anionizing electrostatic field, the field serves the dual function ofprecipitating the particles onto the surface and acting on the depositedparticles as the surface moves therethrough to increase or assistspreading and coalescence of the particles.

The suspension of particles preferably is introduced at such velocity asto form an elongated stream or blanket of substantially uniform widthand thickness in the absence of the electrostatic field, and theparticles are electrostatically deflected toward the object to be coatedand are deposited thereon. By employing a low velocity carrier airstream for the particles I am able to reduce or eliminate ambient aircurrents caused by the carrier Stream, which may cause adventitiousdeposits of parti- Patented Nov. 13, 1956 cles, and insure that theparticles are deposited on the sheet adjacent the leading edge of thefield so that the deposited particles will remain under the coalescingaction of the field for a sufiicient length of time to insure adequatespreading or flow.

The spacing of the deposited particles will depend on their distributionin the stream, and the relative movement between the stream and theobject to be coated. When the sheet or object to be coated is moved pastthe stream of particles, the density or thickness of the coat applied isdetermined by the rate at which the material is supplied and the speedof the web or object to be coated.

In the practice of the present invention I am able to obtain acontinuous liquid coat on the surface of the sheet which is thinner thanany continuous coat heretofore obtained by spray methods. This result Ibelieve is in part due to the nature of the stream or blanket of mistwhich in the absence of an electrostatic field, retains its crosssectional shape for some distance; to the substantially uniform andunidirectional deflecting and depositing action of the electrostaticfield on the mist stream; to the traveling of the web which increasesthe dispersity of the particles deposited; and to the deforming orspreading action of the electrostatic field on deposited particles whichcauses them to spread and to tend to coalesce and form a continuouscoat. The deforming action of the field will vary, depending on thedielectric properties of the liquid particles, their size, the time ofexposure, the strength of the field, and other factors. Under comparableconditions of deposit without an electrostatic field and under thespreading influence of gravity, the particles would form anon-continuous coating. To obtain a continuous coat in the absence of anelectrostatic field it would be necessary to deposit a sufficientlylarge number of particles in overlapping relation so that resultantcontact between particles would induce subsequent flow to an even film.Such a film would contain more material and therefore would be thickerthan that obtained with the same size particles in an electrostaticfield where a greater dispersity of deposit can be secured and becoalesced, in accordance with the present invention. This feature of theinvention is of particular value in instances where excessive coating isdeleterious.

I prefer to bring the particle suspension into the field through aninduction nozzle opening upwardly and which extends generally in thedirection of movement of the object to be coated. This arrangementemploys the force of gravity to oppose the upward momentum of theparticles introduced into the electrostatic field; assists in minimizingthe agitating effect of ambient air currents; and. has the furtheradvantage of avoiding dripping from the nozzle onto the sheet to becoated. In treating sheets; of material the induction nozzle ispreferably of about the same width as the sheet to be coated, and thenozzle opening may be made adjustable so that the apparatus is suitablefor treating sheets or webs of various widths. However, I do not intendto exclude the application of a low velocity diverging stream ofatomized liquid in carrying out the invention.

The preferred embodiment of the atomizer or dispersion producing unitconsists of an air stream type of fluid disintegrator in whichintersecting streams of air and liquid are mingled in a plenum chamber,which may, if desired, contain a bafile or separator unit to break up oreliminate the large particles from the air stream. Where the larger sizeparticles are not a disadvantage the bafliing and separation may beomitted.

According to another feature of the invention, the nebulizing of theliquid takes place in a plenum chamber at super-atmospheric pressure,and the stream of nebulized particles then is introduced into theelectrostatic field, which is in effect in the free atmosphere.

The plenum chamber may be located in or outside the electrostatic field;The provision of a plenum chamber in which the pressure is maintainedintermediate between the pressure of the atornizing liquid or air supplyand the atmospheric pressure provides a space in which-the air and theliquid particles are brought more nearly into velocity equilibrium andmakes it possible to-i'ntroduee' the'strean'r of nebulized liquid intothe electrostatic field at a lower velocity than is possible with airatomizer-s which" carry out the atomization in a one step pressurereduction. This feature of the invention is not limited to thedeposition of a coating of spaced particles, and may be employed fordepositing a continuous or heavy coat in an electrostatic held, andresults in better uniformity ofcoating, more complete utilization ofcoating material, and a higher output of liquid for each dispersionunit. If it is desired to have the atomization occur inthe vicinity ofthe field,- the walls ofthe plenum chamber may serve as a shield againstaction of the electrostatic field.

Where an air stream is employed for producing the dispersion it mayserve as a carrier for the dispersed particles, and if desired, this airstream may be augmented by a supplementary air stream. Al'soit isof'ad'vantage in some cases to provide an auxiliary airstreamthrough theelectrostatic field which serves as an envelope for the stream ofdispersed particles introduced therein. When employing an exhaust fan orthe like for this purpose, there is provided a sub-atmosphericpressurearea in the coating and spreading zone, whichis of benefit in connectionwith the introduction of the low velocity ncbulized liquid from theplenum chamber into the elec trostatic field.

Where the sheet or article to be coated is to be moved through thecoating zone at a speed which may vary from time to time I prefer toemploy a governing arrangement whereby the quantity rate of flow of thenebulized liquid is proportioned with respect to the rate of travel ofthe sheet or web to be coated. In the preferred embodiment this isaccomplished by controlling the fioW-of air to the atomizer inaccordance with the rate of travel of the web or object being coated.The preferred embodiment employs a valved orifice to-control the airsupply to the atomizer which is designed so that the flowthrough theorifice bears a predetermined relationto'the posi tion of the valvetherein. I prefer to employ a pilot load ing source of air pressure togovern-the position of' the valve, which pressure in turn bears apredeterminedor proportional relation to the speed'of travel of the webor sheet to be coated. The pilot loading pressure preferably is obtainedby the back pressure effect in a stream of'air solved natural orartificial waxes or otherjli'quids having dielectric properties whichareof the order-"of these materials.

In particular, when applying'a coating'ofnon-dryin'g or slowly dryingoil, I am ableto deposit athin'ner -film in a given time in anelectrostatic field than when the'force of dielectric oil to coalesce ona surface in an electrostatic field' which if deposited without anelectrostatic field would" surface texture, although it will beunderstood that the nature of the coating applied will be modifieddepending" on the porosity of the web or object,.the relative adheringor wetting. nature of the web or object and the coating material foreach other; and other factors. Thus, for example, the invention isapplicable to the coating of sheet steel with vegetable oil: to producean extremely thin oil coating thereon, to coating paper with a coloredof pigmented molten Wax for the production of copying paper, or coatingof cellophane (regenerated cellulose sheet or film) with a siccativ'eoilor composition for gravity or velocity of a carrier air stream-isemployed field and partly to the action of the electrostatic 'field'in yprecipitating and spreading the dielectric'oil" to cause the depositedparticles to mergeor coalesceonthe'surface to be coated. It thus ispossible to cause particles of rendering it moisture proof, or thewaxing of fruit. Where a non-conducting sheet or object is to be coated,it will be" understood that a conducting backing therefor should beprovided".

The invention will be described in greater detail in connection with theaccompanying drawings. wherein a preferred embodiment of the inventionis disclosed by way of example, and wherein,

Figure l is a side view of a preferred embodiment of the invention,

Figure 2 is'a cross sectional view on li'neII-II of Figure 1',

Figure 3' is a perspective view with parts broken away of a preferredform of atomizer or disperser,

Figure 4 is a partly diagrammatic view of an air pressure transformerfor converting rotational motion into a proportional gas pressure,

Figure 5 is a fragmentary view of an air valve" con troller, and

Figure 6 isa'diagram for explaining the operation of the controllershown in Figure 5.

Referring to Figure 1, there is shown a framework or housinglconstructe'd of channel members and sheets or the like, and extendingfrom the'side walls 2 and 3 are. sets of insulator bars 4 andS (Figures1' and 2) which are secured to the side walls 2, 3 in any suitablemanner. The insulator bars support metal electrode frames 8 and- 9,respectively, which are suitably spaced apart, and each frame supportsone or more'suitable' ionizing electrodes 11 and12, respectively, whichin the preferred embodiment comprise fine wires stretched taut on theframes. However, any suitable construction of ionizing'electrodes may beemployed, which" are connected by frames 8 and 9 and'wires'14'and 15'(Figure 2)to' one output terminal of a high voltage pack (not shown),the Wire lsassing through the insulator bushing'l'd in the end wall 17of to an'exhaust fan '(not shown) of any suitable type. The hood isdivided from the electrostatic field by a distributor or header bathe 21"which-has a series of pe'rforations' 22 todistribute' the suctionaction ofthe hood over' the electrostatic field" and thus roducesrelatively uniform flow of auxiliary air thrbu'ghth'e field.

A strip 26 of cleaned tinned steel passes belo'u'f'and part wayv aroundagrounded idler roll 27. suitably journalled in the housing' 1, andthstr'ip' passes upwardly through the housing between'the electrodeframes '8an'd' 9, .and at the top passes between'a dnv'er roll 28j ahdhold down rolls' 29,30; then" d'ownwardly'to a frying shear'and rollerleveler (not shown). The strip ma also be driven byadrive bridle (notshownlin' advance of roller 27 i The apparatus shown is adapted toapply'acoatingto I At the top of the housing-is located a i both sides of thestrip 26 and includes a pair of induction nozzles 35 and 36 on oppositesides of the strip. However, where coating on only one side of the stripis desired, it will be understood that only one induction nozzle isemployed. The induction spouts or nozzles 35 and 36 receive a supply ofdispersed particles from dispersion units 37 and 38 adjustably mountedupon adjustable support bars 41a and 42a (Figures 1 and 2). The spoutsor nozzles 35, 36 extend in substantially a vertical direction and openupward, so that condensation that occurs within the spouts drips back tothe oil supply, and no dripping can occur from the spouts onto the sheetto be coated. As the dispersion units are alike in construction only onewill be described in detail.

Referring to Figure 3, the dispersion unit 37 comprises a container 41of suitable form, such as a box or tank adapted to contain a liquid.Within the tank are one or more vertical tubes 42, suitably supported ina bracket 43, which provides a small aperture at its upper end 44 andhas its lower end 45 extending into a sump or trough 46 containingliquid to be atomized. The level of liquid will be maintained at afairly uniform level below the upper end 44 of tube 42, by manual orautomatic replenishing means (not shown), and the space 47 above theliquid level serves as a plenum chamber. An air jet pipe 48 enters thetank 41 and supplies a jet of air at its nozzle end 49 at a suitablepressure across the reduced end 44 of tube 42, whereby a stream ofliquid is sucked up into the air jet and is disintegrated or atomized toform a spray. If desired, a heating element 51 of any suitable type maybe located in an insulated housing 52 below the sump to maintain arelatively uniform temperature therein and thus keep the liquid at arelatively uniform viscosity. Additional insulation of the walls ofchamber 37 may be provided, if desired.

The spray 56 is composed of liquid particles of diverse sizesintermingled with air which imparts to the particles a forward velocity.Preferably, a bafile 58, which may be curved as shown, supported bybrackets 59 on the wall of the tank, is interposed in the path of thespray, so that the larger particles in the spray impact against thebafiie and are disrupted into finer particles, or condense thereon anddrip down into the tank. As a result of the baffling and disruptingaction of bafiie 58 and the change of direction of flow of the stream inpassing into the nozzle 35, the particles which are included in the airstream issuing from the induction nozzle 35 are in the form of a finemist or fog. By bringing about atomization of the liquid in a plenumchamber, prior to introduction of the dispersion into the electrostaticfield, I am able to step down the air velocity issuing into theelectrostatic field to reduce or eliminate turbulence therein. The sizeof the plenum chamber and of the nozzle opening may be varied dependingon the pressure gradient desired between the supply pressure and thepressure or velocity of the stream of dispersed particles. The sizeopening of nozzle 35 to the air volume introduced preferably is such asto provide a substantially non-divergent stream of the dispersedparticles passing therethrough as indicated by the dot and dash lines 60(Figure 1) so as to minimize disruption of the stream issuing from themouth of the nozzle. This flow is aided by the auxiliary air stream inthe electrostatic field induced by exhaust duct 19, which sets up in thefield an enveloping, slowly moving stream of air.

While for certain uses the fog thus produced may be carried into theinduction nozzles, I prefer to first dilute the fog by an auxiliary airstream which enters the tank 41 by pipe 61 above the liquid level and ata sufiicient velocity to agitate and dilute the fog, and assist in afurther separation of larger particles. In the preferred embodiment, theair streams in pipes 48 and 61 receive their supply from a commonconduit 65 (Figure 6), and are proportioned by suitable manuallycontrolled valves (not shown). Any number of atomizer units desired maybe contained within the confining chamber 41, two being employed in theembodiment shown. The application or induction nozzle 35 preferably iselongated to about the width of the sheet to be coated, or slightlywider, and if desired, dampers 66 at each end may be provided, thedampers being manually positioned by handles 67 to adjust the width ofthe fog stream issuing from the spouts. These dampers may be locked inposition during operation by any suitable means (not shown). Theionizing zone extends between the ionizing electrodes 11 and 12 and thesheet 26, and it is preferred to have the openings or mouths of theinduction spouts 35, 36 located within this zone.

The operation of the apparatus so far described now will be explained.The sheet 26 of tinned steel is driven through the apparatus at auniform speed. Streams of oil dispersed in air issue from the spouts 35and 36 at a comparatively low rate of flow and the particles of oiltherein are deflected by the electrostatic field and caused to depositon the moving steel strip. Because of the low velocity of the fog ormist entering the electrostatic field and the substantial absence ofturbulent flow between the end of the spout and the deposition area ofthe moving sheet, the particles are moved uniformly toward the sheet bythe electrostatic force, and deposited on the sheet adjacent the edge ofthe field, as indicated at 70. The dispersity on the sheet depends onthe density and velocity of the fog and speed of the sheet. For a givenstream of dispersed particles, a higher sheet velocity will cause theparticles to be deposited in a more disperse spacing. By employing aplenum chamber in which a reduction of pressure of the stream ofdispersed particles occurs I am able to introduce the fog into theelectrostatic field at a reduced velocity. As a consequence theelectrostatically charged particles flow in a curved stream or wallindicated at 70 (Figure 1) which intersects the strip to be coated nearthe leading edge of the field, and the particles coming into contactwith the strip are held thereon by their own wetting action and by theattractive force of the charge of opposite polarity carried by thestrip. Furthermore, in the case of fog particles of a liquid which is arelatively poor conductor, the outer surface of the particles afterbeing deposited may remain charged at the same polarity as the ionizingsource, which would assist in repelling any floating particles in thefield and would cause such floating particles to be deposited on aportion of the strip not previously coated lying between or adjacentparticles already adhering to the strip. In addition the surface chargeupon the free surface of such particles will cause the free surface tobe attracted to the sheet and thus the droplet will be spread so long asthis charge is maintained. Furthermore, the action of the electrostaticfield in lowering the surface tension of the liquid particles depositedon the strip assist in causing relatively poor wetting liquids orliquids of relatively good dielectric properties to adhere to and spreadover and coalesce on the surface of the strip. Thus there is obtained anextremely thin coating of oil on the tinned strip. In explaining thetheory of operation of the apparatus and method, I do not wish to beconfined to such theory in claiming my invention.

While ordinarily the strip travels at a uniform rate through the coatingmachine, there are times, for example, during the automatic welding ofthe ends of two successive strips in the continuous type strip steelmill, when the travel speed is reduced by about one half. Also whenstarting or stopping the operation, there is a gradual deceleration oracceleration of the strip. In the preferred embodiment of the inventionherein disclosed, I regulate or control the volume rate of flow of thefog blanket issuing from the induction nozzle proportionately with thelineal speed of the steel web, so that-a relatively uniform depositionof the particles will be made regardless of variations in the rate oftravel of the steel strip. The mechanism by which this is accomplishednow will be described.

Referrin o Figure a here s Pa t y diagramma ically hown a r hs m s 75which c mp s a vertica ha t c ying a plate 76. ich s ahlv r ve yhorizontal shaft 77 in any suitable manner, and which in turn issuitably driven by a part of the drive mechanism for Sheet 26, such asthe drive bridle. Plate 76 carries two. yokes 81 and 82 in which arepivoted two rocker arms 83 and 84 carrying weights 85 and 86 at theirends. A push rod 87 is suitably supported in the housing 75. and at itslower end carries a collar 88 adapted to be engaged by the ends ofrocker arms 83 and 84. At the top of the housing, a diaphragm 90 issuitably secured by a cover 91 to provide a pressure chamber 92 with aport 9.3 having a conduit 94 connected thereto. Port 93 connects with apassage 95 through the clamped periphery of the diaphragm and terminatesin an Orifice 96. A nozzle 97 is disposed opposite the orifice 96 and isconnected by a suitable flexible coupling 98 to a conduit 99 whichsupplies to the nozzle a stream of air at a constant pressure. As thisapparatus is commercial- 131 available a more detailed description ofits construction is not required.

The operation of the apparatus so far described in connection withFigure 4 now will be explained. At a given sheet speed air issuing fromnozzle 9.7 will enter orifice 96 and through passage 95 will develop apressure in chamber 92 and'conduit 94. Nozzle 97 willassume a positionrelative to orifice 96 such that the force of the air pressure inchamber 92 on diaphragm 90 counterbalances the upward thrust on rod 87due to centrifugal force on weights 85, 86. The pressure in chamber 92is at all times proportional to. the speed of the shaft '77 or strip 26(Figure 1) and therefore the pressure supplied to conduit 94 is alsoproportional to the speed of strip 26.

The pressure in conduit 94 is transmitted to the chamher 101 (Figuresand 6) under a diaphragm 102 con tained within a housing103, a spring104 exerting a bias on the diaphragm. A' push rod 105 engaging diaphragm102 engages a lever 10.6 pivoted at 107, which is urged against abearing member 108. A threaded rod 109 en: gages the bearing'108 and bymeans of a hand wheel 110 thereon, the bearing member can be movedtoward or away from the pivot 107 to vary the mechanical advantage oflever 106.

As previously mentioned, the conduit 65 supplies air to the atomizingdeviceillustrated in detail in Figure 3. This conduit contains a valveindicated generally at 115 which embodies a seat or orifice 116 (Figure5) and a valve closure member 117, the seat and closure being of suchform that the flow through the seat is proportional to the position ofthe closure. The closure is securedto a stem 118 passing through asealing device 119 of suitable construction andabutting adiaphragm 121held between the housing 122 and 'a cover 123; A spring 124 urges thediaphragm 121 upward and urges valve 117 into closed position. A conduit125 supplies a con- 7 stant pressure flow which is conducted by aconduit 126 to pressure chamber 127 and tends to oppose spring 1 24' toopen valve 115.

The housing 128 which receives the conduit 125provides a bleed orifice131' (Figure 6) by which air is bled to the atmosphere and a closure 132secured to lever 133 pivoted at 134 controls the bleed therethrough.Lever 133 and closure 132 are urged to open position by a spring 135,and a spring ferrule 136-is securedto a bar 137 which in turn is seeuredto valve rod 118. The ever 133 is urged by spring 135 into engagementwith hearing member 108 A finger wheel 133permits man I ual adjustmentofspring 135.

The operation of the control apparatus now will be described. Assumingthe sheet '26 is moving at a constant speed, the pressure in chamber 92(Figure and in conduit 94 is constant and is proportional to the speedof s t 2 h s ihfli s i' s f h m as s $2 ,1 1.91

r 1 21 ondu te here o. y cond it. 4.. he d a hra m w l tak up a ns ti Qta s st h ih hr h Pr s e i ch mb r 9 ps esl hr th bias. d smiss;

.5. which n has de ends on the n s t f' a t rs 1 a valve 5;. T w t sh 0fssure 3. elative to orifice 131 will similarly be established by thesetwo conditions. Under conditions of fined bleed at oris 3 e. nr h s n haw l d te m hs h position of valve and thus determine the rate of flow ofair through conduit 65 to the pipes 61 and 48. When h eet a mes lowerspeed, t e sh h s in ih a fetch h W i t 8 a d .6. sa ers t m inorsinward and allows nozzle to take up a new position of balance with orifce 96 so that the pressure in chamher 9Z'JCQndHit a t ambe 01 draw t fsat' ahish l s Spring 1 t PM ev r 1 3 siswhwarsi is move closure 132further from orifice 131 to allow a greater bleed therethrough, whichresults in a reduction of l di p shreih chambe n a urther s:

s ia al e 9 r duc t flow of air throu h conduit 65 to the atomizingdevice. Valve 115. under h coh is W 'I??l ?h a n w o it o of 1 13 91?which the flow of air to the ato rn izing device 37 is pro} P -ha he enshred o heet 26- Whsn peed r Sheet 26' i sr a a an a ti n se t th bo es:

scribed will again establish the proper relation between sa s-d ofs'shse and the flaw o air o th at z: s dev e BY n s atihs h 11 W f. a th atQm z-- ing device with the speed of the sheetpthe flow of mi s ma eial su n f m zle 3. s ikew s rre at d. q l s s ih s 9 the heet speed tobta n a consistently the sheet speed.

Various modifications may be made in the invention ssr h sl it u d ar nm h p rit n shops srss ii hh rsths h h sih mean fqrmo in a iss 9 hesatsr qaia h' means i proshnhy to a ast has htfes sf, sa d hhisc m psfor prq hs na a SPmiQ 9 quid a tis s n a as stream a c hduit forintroduei g a str m of d ersed part b w n eshis t a d ihh zihs insane sad ehdui erminatin in the 99 Pa h be ween h n in means an Q i et to l ases i she th in h sm Path a d-m aslcoorditlh t e t 9 fl w Q s id s ream Q'di per ed-par: is w t the s ee f a d hhiest- 2 Airapparatuscomprisingrneans for moving an ob-s ject presenting esurfacejto be coated, electrostatic? ionizingmeans in proximity to saidsurface,' means for intro duping finely divided material into theelectrostatic remfor deposit upon said surface, and meanscoordinatingthe speed of said surface and rate of fiow of said finelyyided material.

3( An' apparatus comprising means for moving anobject'presenting asurface to be coated, gas ator'nizing means for producing a suspensionof iin'el'y divided par ticles in a g'as st'rear'n, a gas conduit forsupplying gas tgosaid atomi'zing means, valve means in said condiiit tocontrol the How of 'in p redeterihinedrelation totthe' position of thevalve thereof, a gas pressure contrpl am e h said v ve avihaa b e lth rr m, me

connected to said valve to, vary said bleed; 'and means uhif hh de s oma r a nde e dent at I responsive to the speed of said surface andconnected to said last named means to vary said bleed.

5. An apparatus comprising, means for moving an object to be coated,ionizing means in proximity to at least one surface of said object forproducing and moving ions in a path toward said surface, means forproducing a dispersion of liquid particles in a gas, a containersurrounding said dispersion-producing means, an induction nozzleextending from said container into said ion path, said container andnozzle being of electrically conducting material and serving toelectrically shield said dispersion as it is produced and conducted inthe gas stream from the container to the ion path.

6. In an electrostatic coating apparatus in Which electrically chargedparticles of liquid coating material in a coating zone areelectrostatically deposited on the surface of an object passing throughsuch coating zone, means for moving the object through the coating zone,coating-material supply means, a high-voltage source for creatingelectrical charges of opposite signs on the object and coating materialparticles, and a control device responsive to the rate of movement ofsaid object through the coating zone and controlling said supply meansto maintain a predetermined ratio between the speed of said surface andthe rate of coating-material supply.

7. In an electrostatic coating apparatus in which electrically chargedparticles of liquid coating material in a coating zone areelectrostatically deposited on the surface of an object passing throughsuch coating zone, means for moving the object through the coating zone,coating-material supply means having a discharge orifice, a high-voltagesource for creating electrical charges of opposite signs on the objectand coating material particles, and a control device controlling saidsupply means and coordinating With the speed of said surface both theVelocity and quantity-rate at which coating material is dischargedthrough said orifice.

References Cited in the file of this patent UNITED STATES PATENTS738,347 Myers Sept. 8, 1903 1,788,600 Smyser Jan. 13, 1931 1,855,869Pugh Apr. 26, 1932 2,047,525 Thode July 14, 1936 2,078,790 Bucy Apr. 27,1937 2,159,351 Burns May 23, 1939 2,187,837 Paasche Jan. 23, 19402,191,827 Benner Feb. 27, 1940 2,221,338 Wintermute Nov. 12, 19402,334,648 Ransburg Nov. 16, 1943 2,421,787 Helmuth June 10, 19472,447,664 Pegg Aug. 24, 1948

